This invention relates to a method of and apparatus for packaging, and more particularly to a packaging method and apparatus of the form, fill and seal type.
The invention is especially concerned with a method of packaging of the type in which receptacles are formed (e.g., vacuum-formed) in a web of thermoformable flexible sheet plastic material, units to be packaged (e.g., slices of bacon on a card) are introduced one-by-one into the receptacles, and a web of thermoplastic flexible sheet plastic material is sealed to the formed web to produce hermetically sealed packages, and with a machine for carrying out the method, the machine being of the type having an endless series of dies or molds (e.g., on a wheel) in which the receptacles are formed. Reference may be made to U.S. Pat. No. 2,935,828 issued May 10, 1960 showing a prior machine of this type, the present machine involving improvements over this prior machine.
In the utilization of the continuous-motion wheel-type vacuum packaging machine, as for example in vacuum packaging bacon, the machine must generally be operated at such a speed as to accommodate what is referred to as the "instantaneous line speed" of the operation, which is the rate at which units to be packaged arrive at the machine for a short interval of time. This is distinct from the "average line speed", which has reference to the average number of units arriving to be packed in a given period of time. Generally, the machine is set to operate at a speed somewhat higher than the "instantaneous line speed" to avoid any problem of product back-up when the units are arriving at "instantaneous line speed." The problem is intensified when two supply lines are used to feed one packaging machine (e.g., when two bacon slicing lines are used to feed one packaging machine).
Provision may be made for accommodating the machine to different infeed speeds by providing it with a speed control means adapted to be set by the operator of the machine to run it at different speeds, e.g., at a high speed or a medium speed (and "stop"). Thus, the machine may have control means for running it at high speed for packaging 80 units per minute, for example, or at medium speed for packaging 60 units per minute, for example. The operator changes the speed according to her observation of the infeed of the units to the packaging machine. If units are accumulating, she sets the machine to run at high speed; if the accumulation is diminishing, she sets it to run at medium speed. If no units are coming, she stops the machine. This has advantages including enabling an operator to load units onto the infeed conveyor at a more consistent and slower pace, reducing the possibility of producing empty packages, increasing the efficiency of the packaging machine, less reworking (bad packages) and less machine maintenance.
Prior machines have been such, however, that the sealing time interval for each package (i.e., the time in which the "unformed" or "cover" web for the package is sealed to the formed web) has been inversely proportional to the speed of operation of the machine, more particularly the speed of rotation of the mold wheel. That is, in prior machines on increasing the speed of the wheel the sealing time is inherently decreased, leading to the problem that the seals on packages made at high speed may not always be satisfactory.